Datasheet

TMC236/A/B DATA SHEET (V2.10 / 2016-Jun-06) 26
Copyright © 2004, TRINAMIC Motion Control GmbH & Co KG
Application Note: Extending the Microstep Resolution
For some applications it might be desired to have a higher microstep resolution, while keeping the
advantages of control via the serial interface. The following schematic shows a solution, which adds
two LSBs by selectively pulling up the SRA / SRB pin by a small voltage difference. Please remark, that
the lower two bits are inverted in the depicted circuit. A full scale sense voltage of 340mV is assumed.
The circuit still takes advantage of completely switching off of the coils when the internal DAC bits are
set to “0000”. This results in the following comparator trip voltages:
Current setting
(MSB first)
Trip voltage
0000xx
0 V
000111
5.8 mV
000110
11.5 mV
000101
17.3 mV
000100
23 mV
...
111101
334.2 mV
111100
340 mV
SPI bit
15
14
13
12
11
10
9
8
DAC bit
/B1
/B0
/A1
/A0
MDA
A5
A4
A3
SPI bit
7
6
5
4
3
2
1
0
DAC bit
A2
PHA
MDB
B5
B4
B3
B2
PHB
R
S
SRA
TMC236 /
TMC239
110R
4.7nF
opt.
74HC595
C1
Q0
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q7'
/MR
C2
/OE
SCK
SDI
SDO
CSN
+V
CC
DS1D
100K
/CS
SDI
SCK
SDO
Free for
second
TMC239
47K 47K
47K
/DACA.0
/DACA.1
/DACB.0
/DACB.1
Vcc = 5V
1/2 74HC74
C
DQ
Note: Use a 74HC4094
instead of the HC595 to get
rid of the HC74 and inverter
Please see the FAQ document for more application information.